Method and apparatus for switching of shunt and through switches of a transceiver

ABSTRACT

A switching network and associated method for operating within a transceiver are disclosed. The switching network has a timing control circuit that offsets the time at which a through switch and a shunt switch transition between on and off states. The output of the timing control circuit is an inverted and delayed version of a control signal applied to the input of the timing control circuit. Controlling the timing of the shunt switch provides a means to safely discharge any accumulated charge within the capacitance C gs  between the gate and source of transistors included within the through switch.

CROSS-REFERENCE TO RELATED APPLICATIONS—CLAIM OF PRIORITY

This application is a continuation of, and claims the benefit ofpriority under 35 USC § 120 of, commonly assigned and prior U.S.application Ser. No. 16/352,647, filed Mar. 13, 2019, entitled “Methodand Apparatus for Switching of Shunt and Through Switches of aTransceiver”, the disclosure of which is incorporated herein byreference in its entirety. Application Ser. No. 16/352,647 is acontinuation of, and claims the benefit of priority under 35 USC § 120of, commonly assigned prior U.S. application Ser. No. 15/612,941, filedJun. 2, 2017, “Method and Apparatus for Switching of Shunt and ThroughSwitches of a Transceiver”, now U.S. Pat. No. 10,277,268 issued Apr. 30,2019, the disclosure of which is incorporated herein by reference in itsentirety.

BACKGROUND (1) Technical Field

This disclosure relates to transceivers, and more specifically tomethods and apparatus for switching between transmit mode and receivemode within a transceiver.

(2) Background

In many instances today, a single antenna is connected to a transceiverfor both transmission and reception. FIG. 1 is a simplified illustrationof some of the components of one such transceiver 100. The transceiver100 includes an antenna 102 connected to the first port 104 of athree-port Radio Frequency (RF) circulator 106. A three-port circulatorhas a relatively low impedance for signals between counter-clockwiseadjacent ports and a relatively high impedance between clockwiseadjacent ports. Accordingly, there is a low impedance path through thecirculator from the first port 104 to the second port 108. Likewise,there is a relatively low impedance from the second port 108 to thethird port 124 and from the third port 124 to the first port 104.However, in the other direction through the circulator, there is arelatively high impedance from the first port 104 to the third port 124,from the third port 124 to the second port 108 and from the second portto the first port 104.

The second port 108 of the circulator 106 is coupled to the receiversection 110 of the transceiver 100 and to a detector section 111.Looking first at the receiver section 110, the second port 108 of thecirculator 106 is coupled to a first port of a “through switch” 112within the receiver section 110. In some cases, the through switch 112is a field effect transistor (FET), and the first signal port of thethrough switch 112 is the drain of the FET. The receiver section 110further includes a direct current (DC) blocking capacitor 114, a lownoise amplifier (LNA) 116, a shunt switch 118 and a bias control circuit120. In the case in which the through switch 112 is a FET, the secondsignal port is the source of the FET of the through switch 112. In somecases, the drain and source of the FET of the through switch 112 areinterchangeable. The source is coupled to a first terminal of the DCblocking capacitor 114. A second terminal of the DC blocking capacitor114 is coupled to the input of the LNA 116.

A first signal port of the shunt switch 118, which in some cases is thedrain of a FET, is also coupled to the source of the through switch 112.The second signal port is the source of the FET shunt switch 118. Thesource is coupled to ground. In receive mode, the shunt switch 118 andthe through switch 112 work together to couple signals from the antenna102 to the input of the LNA 116. That is, by turning on the throughswitch 112 and turning off the shunt switch 118, signals receivedthrough the antenna 102 are routed from the first port 104 of thecirculator 106 to the second port of the circulator 108. The signalsthen follow the low impedance path through the through switch 112. Therelatively high impedance of the non-conducting (“OFF”) shunt switchblocks the signal from shunting to ground. It should be noted thatthroughout this disclosure, the term “on” is used to refer to theoperational state of a FET or other switching device in which there is alow impedance between the drain and source (or in non-FET devices,between the switch terminals). Likewise, the term “off” is used to referto the operational state in which a high impedance is presented betweenthe switch terminals (e.g., drain and source).

Looking next at the detector section 111, a similar arrangement ofswitches 113, 115 provides a path from the second port 108 of thecirculator 106 to a 50 ohm detector 117 within the detector section 111when the switch 113 is on and the switch 115 is off. The same signalthat turns on the shunt switch 118 of the receiver section 110 iscoupled to the control port to turn on the switch 113 in the detectorsection 111. Likewise, the switches 112 and 115 are controlled by thesame signal. Therefore, when the switch 112 in the receiver section 110is off, the switch 115 in the detector section 111 is also off.Accordingly, either the LNA 116 of the receiver section 110 or thedetector 117 of the detector section 111 is coupled to the second outputof the circulator 106 at any particular time. More particularly, whenthe transceiver 100 is in receive mode, the LNA 116 of the receiversection 110 is coupled to the port 108 of the circulator 106 and theinput to the detector 117 is shunted to ground. When the transceiver 100is in transmit mode, the detector 117 is coupled to the port 108 of thecirculator 106 and the input to the LNA 116 is shunted to ground. The 50ohm detector 117 provides a proper load for the circulator 106.

RF signals traverse the relatively low impedance path through the DCblocking capacitor 114 and are applied to the input of the LNA 116. Inthe case shown in FIG. 1, the bias control circuit 120 provides DC biasto the input of the LNA 116. In some cases, a timing processor 126determines when the transceiver 100 is in transmit mode and when thetransceiver 100 is in receive mode. The timing processor 126 can be assimple as some circuitry in the modulator/demodulator of the transceiverfor determining when data is ready to be sent. Alternatively, the timingprocessor 126 can be a more sophisticated programmable device thatdetermines the mode of the transceiver 100 based on several factors. Thetiming processor 126 provides a control signal 128 to the bias controlcircuit 120. In some cases, the bias control circuit 120 provides a biasthat is appropriate to the mode of the transceiver (e.g., transmit orreceive), as indicated by the control signal 128. The through switch 112is turned on by applying a mode control signal V_(on) to the controlport (e.g., the gate) of the through switch 112. In some cases, thesignal V_(on) is generated by the timing processor 126. An inverse modecontrol signal V_(on) that is the inverse of the signal V_(on) isapplied to the control port (e.g., the gate) of the shunt switch 118.Thus, when the through switch 112 is turned on, the shunt switch 118 isturned off (assuming both FETs 112, 118 are the same, i.e., eitherP-channel or N-channel FETs).

The transceiver 100 further includes a transmit amplifier 122 that iscoupled to the third port 124 of the circulator 106. In transmit mode,the transmit amplifier 122 outputs a transmit signal that is coupledthrough the third port 124 of the circulator 106 to the first port 104of the circulator 106. As noted above, the circulator 106 has arelatively high isolation between the input to the third port 124 andthe output from the second port 108. Therefore, the power applied to theinput port 124 is principally coupled to the antenna 102. Nonetheless,in order to protect the LNA 116, the through switch 112 disconnects theLNA 116 from the antenna 102. In addition, the shunt switch 118 furtherisolates the input of the LNA 116 by coupling the input of the LNA 116to ground through the DC blocking capacitor 114 and the shunt switch118. Any power that is inadvertently coupled to the second port 108 ofthe circulator is isolated from the input of the LNA 116 by the highimpedance between the drain and the source of the through switch 112,which is off during transmit mode and also by the low impedance toground presented by the shunt switch 118 which is on during transmitmode.

When implementing the through switch 112 and the shunt switch 118 as FETswitches, the through switch 112 must be capable of sustaining arelatively high drain to source voltage without breaking down.Therefore, the through switch 112 must be relatively large. Typically,this is implemented by stacking several individual FETs together to formthe through switch 112. The number of FETs that are stacked depends uponseveral factors, including the drain to source voltage that the switch112 is designed to withstand. In some cases, the shunt switch 118 alsocomprises several stacked FETs.

Each FET of the through switch 112 has a capacitance C_(gs) between thegate and source. These capacitances C_(gs) are in parallel. Therefore,the capacitance C_(gs) of each FET sums to form a total capacitancebetween the control terminal of the through switch 112 and the input ofthe LNA 116. When the through switch 112 changes state from off to on,the voltage swings from −V to +V for a total swing of 2V. That voltage,multiplied by the capacitance C_(gs), determines the charge Q that isapplied to the input of the LNA 116. In light of the relatively largevalue of the capacitance C_(gs), the charge Q applied to the input ofthe LNA 116 can be substantial. In some cases, it could increase thegate voltage at the LNA input to an unsafe value. In some cases, thislarge voltage can cause a breakdown of the input of the LNA 116.

FIG. 2 is graph showing the voltage V_(g) applied to the input of theLNA 116 at the time the transceiver transitions from transmit mode toreceive mode. FIG. 2 also shows the transition of the state of thesignals V_(on) and V_(on) . As can be seen in FIG. 2, prior to time t₀,the DC component of the voltage V_(g) is at (or near) the transmit modebias level (i.e., the voltage provided from the bias control circuit 120to the LNA input during the transmit mode. Any RF component of thesignal that is present is disregarded for the purpose of this analysis).At time t₀, the signal V_(on) begins to transition from a low state,V_(low) to a high state, V_(high). Since the signal V_(on) is theinverse of the signal V_(on), the signal V_(on) will also start totransition from a high state, V_(high), to a low state, V_(low).Accordingly, the charge that has been stored in the capacitance C_(gs)of the through switch 112 will cause the voltage V_(g) to rise as thethrough switch 112 starts to conduct and the shunt switch 118 turns off.In addition, the bias control circuit 120 attempts to transition thebias voltage at the input of the LNA 116 to a receive mode bias level.The voltage V_(g) rises to a peak at time t₁, primarily as a consequenceof the charge stored in the capacitance C_(gs) of the through switch112. Starting at time t₁, the voltage V_(g) decreases until at time t₂the voltage Vg reaches the receive mode bias level established by thebias control circuit 120. Finally, at time t₃, the voltage stabilizes atthe desired receive mode bias level.

There are two principle problems with the current transceiver 100. Thefirst is that the amount of charge stored in the capacitance C_(gs) ofthe through switch 112 can be sufficiently great that the voltage V_(g)at time t₁ damages the LNA input (i.e., breaks through the gate of theinput FET of the LNA 116). The second problem is that during therelatively long time between t₀ and t₃ the LNA bias is disturbed,leading to fluctuations in the operation of the LNA 116, such asincreased non-linear behavior. That is, the amount of time it takes tostabilize V_(g) at the receive mode bias level, causes the operation ofthe LNA 116 to vary for an undesirable amount of time.

It can be seen that there is currently a need for a method and apparatusthat reduces the risk of damage to the input of an LNA of a transceiverduring transitions from transmit mode to receive mode. In addition,there is a need for a method and apparatus that reduces the amount ofvariation at the LNA output during the transition to receive mode. Thepresent disclosure presents a method and apparatus that meets this need.

SUMMARY

A transceiver and associated method for operating the transceiver aredisclosed. The transceiver and disclosed method mitigate againstdistortion at the LNA output and an undesirable rise in the voltage atthe input to an LNA of the transceiver when the transceiver transitionsfrom transmit mode to receive mode. In particular, the transceiver has atiming control circuit that offsets the time at which a through switchand a shunt switch transition between on and off states. The output ofthe timing control circuit is an inverted and delayed version of acontrol signal applied to the input of the timing control circuit. Bycontrolling the timing of the shunt switch with respect to the throughswitch, the voltage applied to the input of the LNA can be maintained atsafe levels. In particular, controlling the timing of the shunt switchprovides a means to safely discharge any accumulated charge within thecapacitance C_(gs) between the gate and source of transistors includedwithin the through switch.

The details of one or more embodiments of the disclosed method andapparatus are set forth in the accompanying drawings and the descriptionbelow. Other features, objects, and advantages of the invention will beapparent from the description and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified illustration of some of the components of atransceiver in accordance with at least one embodiment of the disclosedmethod and apparatus.

FIG. 2 is graph showing the voltage V_(g) applied to the input of an LNAover time as the state of signals V_(on) and V_(on) transition, causingthe transceiver to transition from transmit mode to receive mode.

FIG. 3 is a simplified illustration of a transceiver having an antennathat is shared by a receiving section and a transmit amplifier.

FIG. 4 is a schematic of one embodiment of the timing control circuit.

FIG. 5 is a graph illustrating the timing of the signals V_(on) andV_(on) and the resulting voltage, V_(g).

FIG. 6 is a graph showing the signals Von, V_(on) , Vg as thetransceiver transitions from receive mode to transmit mode.

FIG. 7 is an illustration of an alternative embodiment in which aninductor is placed between the source of the shunt switch and ground.

FIG. 8 is a simplified flowchart of a process in accordance with someembodiments of the disclosed method and apparatus.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 is a simplified illustration of a transceiver 300 having anantenna 102 that is shared by a receiving section 302 and a transmitamplifier 122. The transceiver 300 further includes a three-portcirculator 106, a timing processor 308 and a timing control circuit 310.Similar to the circulator 106 show in FIG. 1 and discussed above, thecirculator 106 couples transmit signals from the transmit amplifier 122to the antenna 106. In addition, signals that are received by theantenna are coupled by the circulator 106 to the receive section 302 ofthe transmitter 300. It will be understood by those skilled in the artthat other types of devices can be used to direct the power from thetransmit amplifier 122 to the antenna 102 and to couple signals receivedby the antenna 102 to the receiving section 302. The circulator 106 ismerely shown as one example of a device used in a transceiver inaccordance with the disclosed method and apparatus.

The timing processor 308 is any programmable controller, microprocessor,state machine, or any discrete hardware and/or firmware that is capableof receiving and/or generating information regarding when thetransceiver 300 is to be in receive mode versus when the transceiver 300is to be in transmit mode and for generating a mode control signalV_(on) and an input signal to the bias control circuit 306. In someembodiments, the timing processor 308 is integrated into themodulator/demodulator of the transceiver 300. The particular mechanismused by the timing processor 308 to determine when the transceiver 300is in transmit mode and when the transceiver 300 is in receive mode iswell-known. Therefore, for the sake of simplicity and efficiency, thedetails of the operation of the timing processor 308 are not disclosedherein. However, those skilled in the art will know how to provide sucha timing processor 308 for performing the functions disclosed. Thereceiving section 302 of the transceiver 300 includes a through switch112, DC blocking capacitor 114, LNA 116, shunt switch 118 and biascontrol circuit 306. The combination of the receiving section 302,timing processor 308 and timing control circuit 310 can be referred toas a switching network within the transceiver 100.

FIG. 4 is a schematic of one embodiment of the timing control circuit310. In some embodiments, the timing control circuit 310 outputs aninverse mode control signal V_(on) . The inverse mode control signalV_(on) is an inverted and delayed version of the signal V_(on). In someembodiments, the timing control circuit 310 includes three invertergroups 401, 403, 405, a bypass switch 410, and an RC delay circuit 412.The first inverter group 401 includes an even number of inverters. Inthe embodiment shown in FIG. 4, there are two inverters 402, 404 in thefirst inverter group 401. However, it will be understood that any evennumber of inverters can be used, depending upon the amount of delay tobe provided through the first inverter group 401. The output of thefirst inverter group 401 is coupled to the input of the RC delay circuit412. Since the first inverter group 401 has an even number of inverters,the delay circuit input signal is a delayed version of the mode controlsignal with no inversion. In some embodiments, the second inverter group403 has one inverter 408. However, it will be understood that the secondinverter group 403 can have any odd number of inverters that is lessthan the number of inverters included in the first inverter group 401.The third inverter group 405 also has an odd number of inverters. Whileonly one inverter 406 is shown in FIG. 4, any odd number can be used.

The RC delay circuit 412 includes a resistor 414 and a capacitor 416. Inthe embodiment shown in FIG. 4, the bypass switch 410 is a FET. Thedrain of the FET 410 is coupled to input of the RC delay circuit 412.The source of the FET 410 is coupled to the output of the RC delaycircuit 412. Accordingly, when the FET 410 is conducting, the FET 410establishes a low impedance bypass path around the RC delay circuit 412.The gate of the FET 410 is coupled to the output of the second invertergroup 403. The output of the second inverter group 403 is a bypasscontrol signal. It can be seen that the bypass control signal is,therefore, a delayed and inverted version of the mode control signalV_(on). In some embodiments, the delay imposed on the mode controlsignal V_(on) by the second inverter group 403 is shorter than the delayimposed by the first inverter group 401 (i.e., there are few invertersin the second inverter group 403 than in the first inverter group 401).

When the mode control signal V_(on) changes from a low voltage to a highvoltage, the signal applied to the gate of the FET 410 goes from high tolow, and the FET 410 turns off (i.e., operates with high impedancebetween the drain and source). Turning off the FET 410 removes thebypass path. In some embodiments, the delay imposed by the firstinverter group is longer than the delay imposed by the second invertergroup 403. This ensures that when the mode control signal V_(on) goeshigh, the FET 410 has sufficient time to turn off and stop conductingbefore the output of the first inverter group 401 changes state. Thehigh impedance path provided by the FET 410 places the delay circuit 412in the signal path. Therefore, the RC time constant of the combinationof the resistor 414 and the capacitor 416 will determine the rise timeof the signal at the input of the third inverter group 405. The valuesof the resistor 414 and capacitor 416 are set to establish a desireddelay in the transition of the inverse mode control signal V_(on) fromhigh to low with respect to the transition of the mode control signalV_(on) from low to high.

The third inverter group 405 has an odd number of inverters.Accordingly, the output V_(on) of the timing control circuit 310 is theinverse of the input V_(on) to the circuit 310. In addition, in someembodiments, the output stage of the third inverter group 405 has arelatively fast rise and fall time to ensure that the inverse modecontrol signal V_(on) will have a relatively fast transition, once thattransition occurs.

On the other hand, when the mode control signal V_(on) changes statefrom a high voltage state to a low voltage state, the FET 410 will turnon, providing a low impedance bypass path around the RC delay circuit412 (i.e., from the output of the second inverter 404 to the input ofthe third inverter 406). By establishing a bypass path around the RCdelay circuit 412, the FET 410 reduces the amount of delay between thetransition of the mode control signal V_(on) and the transition of theinverse mode control signal V_(on) . It should be noted that some delaywill exist due to the three inverters 402, 404, 406. In someembodiments, the delay imposed by the RC delay circuit 412 when the FET410 is not conducting is substantially greater than the delay of theinverters 402, 404, 406. Accordingly, the delay between the transitionof V_(on) from low voltage to high voltage and the transition of V_(on)from high voltage to low voltage will be greater than the delay betweenthe transition of V_(on) from high voltage to low voltage and thetransition of V_(on) from low voltage to high voltage. That is, theinverse mode control signal V_(on) changing from high to low is delayedmore than when the inverse mode control signal V_(on) changes from lowto high.

Returning once again to FIG. 3, it can be seen that V_(on) is coupleddirectly to the control port (i.e., the gate) of the through switch 112from the timing processor 308. On the other hand, V_(on) is generated bythe timing control circuit 310 and is delayed when transitioning from afirst state (i.e., a high voltage) to a second state (i.e., a lowvoltage). Accordingly, when the timing processor 308 causes thetransceiver 300 to change from transmit mode to receive mode, thethrough switch 112 will turn on some time before the shunt switch 118turns off. In addition, the timing processor 308 will turn the transmitamplifier 122 off before turning the through switch 112 on. The delay inturning off the shunt switch 118 allows the charge that accumulated inthe capacitance C_(gs) of the FETs within the through switch todischarge through the shunt switch 118 to ground before the shunt switch118 is turned off. In some embodiments, the delay is sufficiently longto permit at least 50% of the charge accumulated in the capacitanceC_(gs) to discharge before the shunt switch is opened. In otherembodiments, the delay is sufficiently long to allow 75% of the chargeaccumulated in the capacitance C_(gs) to discharge before the shuntswitch is opened. In another embodiment, the delay is sufficiently longto allow 95% of the charge accumulated in the capacitance C_(gs) todischarge before the shunt switch is opened. In some embodiments, thedelay is 50 ns.

FIG. 5 is a graph illustrating the timing of V_(on) and V_(on) and theresulting voltage, V_(g). V_(on) and V_(on) are shown in separate graphsin FIG. 5 to make it easier to see the shape of each signal. As shown inFIG. 5, at time t₀, the mode control signal V_(on) generated by thetiming processor 308 begins to rise. As V_(on) rises, it turns on thethrough switch 112, beginning the process of switching the transceiver300 to receive mode. As noted above, when V_(on) transitions to a highvoltage level, the FET 410 within the timing control circuit 310 turnsoff. Turning off the FET 410 causes the RC delay circuit 412 to delaythe rise of the signal at the input of the third inverter 406 withrespect to the rise of V_(on). Accordingly, V_(on) output from the thirdinverter 406 does not begin to fall until time t₂. As shown in FIG. 2and FIG. 5, t₂ occurs after the charge accumulated within thecapacitance C_(gs) of the through switch 112 has been discharged throughshunt switch 118, due to the delay in V_(on) . That is, the shunt switch118 remains on (i.e., is conducting) between time t₀ and time t₂. Attime t₂, V_(on) starts to fall. It should be noted that the inverse modecontrol signal V_(on) is provided by the output of the third inverter406 (shown in FIG. 4). In some embodiments, providing an inverter 406with a relatively fast transition from high to low yields an inversemode control signal V_(on) with a shorter transition period than themode control signal V_(on).

The timing processor 308 provides a signal 312 to the bias controlcircuit 306 indicating the mode of operation (i.e., receive mode ortransmit mode). The signal 312 causes the bias control circuit 306 toset the bias to the input of the LNA 116 to the appropriate level forthe LNA 116 to operate in the indicated mode. Due to the delay in thetransition of V_(on) , the voltage V_(g) remains at the transmit modebias level until time t₂. At time t₂, the voltage V_(g) starts to riseto the receive mode bias level set by the bias control circuit 306. Withthe transceiver 300 in receive mode, thru switch 112 is on and the shuntswitch 118 is off. Therefore, an RF signal coupled through the DCblocking capacitor 114 to the input of the LNA 116 is superposed on theDC bias level set by the bias control circuit 306.

In some alternative embodiments, the signal 312 provided to the biascontrol circuit 306 is V_(on). In such embodiments, the bias controlcircuit 306 changes the bias level provided to the input of the LNA 116in response to V_(on). In some such cases, the timing of the change inbias voltage provided to the LNA 116 from the bias control circuit 306can be set within the bias control circuit 306 to take into account whenthe through switch 112 and/or the shunt switch 118 change state toensure that the bias transitions smoothly from the transmit mode biaslevel to the receive mode bias level.

Delaying the fall of V_(on) ensures that the shunt switch 118 remains onlong enough for the charge on the capacitance C_(gs) to be shunted toground through the shunt switch 118. In addition, the receive mode biaslevel V_(g) at the input of the LNA 116 is achieved quickly upon theshunt switch 118 turning off, since the effects of the charge stored inC_(gs) have been mitigated by the shunt switch 118. Therefore, the LNA116 achieves linear operation quickly once the transceiver switches fromtransmit mode to receive mode. It should be noted that while the throughswitch 112 and the shunt switch 118 are shown as p-channel FETs, othertypes of transistors, and in fact, other types of semiconductor switchesmay be used. Furthermore, in alternative embodiments, the through switch112 and the shunt switch 118 may not be the same type of switch. Byreplacing the inverter 406 with a non-inverting buffer, the throughswitch 112 and the shunt switch 118 can be fabricated such that one ofthe switches has a p-channel and the other has an n-channel.Accordingly, one turns on with a high voltage applied to the gate, whilethe other turns on with a low voltage applied to the gate.

FIG. 6 is a graph showing Von, V_(on) , Vg as the transceivertransitions from receive mode to transmit mode. While the timing controlcircuit 310 generates V_(on) with a slight delay d with respect toV_(on) (i.e., V_(on) starts to rise slightly after the V_(on) starts tofall), the amount of delay is greater when transitioning from a firststate in which the shunt switch is closed (i.e., from receive mode) to asecond state in which the shunt switch is open (i.e., to transmit mode).In addition, in some embodiments, having a relatively fast inverter 406at the output of the timing control circuit 310 can compensate for thisslight delay d. Accordingly, the shunt switch 118 is turned on at nearlythe same time as the through switch 112 is turned off, providingisolation of the LNA 116 from stray signals as soon as possible.Accordingly, in such embodiments, the output of the timing controlcircuit 310 is delayed only when transitioning from a first state inwhich the shunt switch is closed to a second state in which the shuntswitch is open. In addition, the bias control circuit 306 changes theLNA bias from the receive bias mode level to the transmit bias modelevel. The result is that V_(g) transitions quickly from the receivemode bias level to the transmit mode bias level.

FIG. 7 is an illustration of an alternative embodiment in which aninductor 702 is placed between the source of the shunt switch 118 andground. The inductor 702 provides a low impedance path for the charge inthe through switch to dissipate, while providing a high impedance forsignals that are coupled to the receiver section 302 from the antenna102.

FIG. 8 is a simplified flowchart of a process in accordance with someembodiments of the disclosed method and apparatus. The process startswith the transceiver 300 in transmit mode. The timing processor 308waits for a determination that the transceiver 300 is to transition fromtransmit mode to receive mode (STEP 802). Upon making the determinationthat the transition is to occur, the timing processor 308 causes V_(on)to transition from a relatively low voltage to a relatively high voltage(STEP 804). V_(on) is applied to the timing control circuit 310 (STEP806). The timing control circuit 310 delays and then inverts V_(on) togenerate V_(on) (STEP 808). V_(on) is coupled to a control port of thethrough switch 112 (such as the gate of a FET, in some embodiments) andturns the through switch 112 on (STEP 810). V_(on) is coupled to acontrol port of the shunt switch 118 (such as a gate of a FET, in someembodiments) and turns the shunt switch 118 off a predetermined amountof time after the through switch 112 is turned on (STEP 812). In someembodiments, the predetermined amount of time is at least long enoughfor a sufficient amount of the charge that has accumulated in thecapacitance C_(gs) of the through switch 112 to discharge through theshunt switch 118 that the voltage applied to the input of the LNA 116upon the shunt switch opening, does not damage the LNA 116. In someembodiments, the predetermined amount of time is sufficiently long thatthe voltage applied to the input of the LNA 116 by the bias controlcircuit 306 will not significantly overshoot the receive mode bias levelwhen the shunt switch 118 opens. In some embodiments, a “significantovershoot” occurs if the voltage peaks at more than 110% of the receivemode bias level. In other embodiments, “significant overshoot” occurs ifit takes more than 66% of the time required for the signal to go from aminimum voltage to a maximum voltage before settling to within 95% ofthe receive mode bias voltage. These parameters are provided as examplesand not intended to be followed in all embodiments.

In some embodiments, the process further includes making a determinationthat the transceiver 300 is to transition from receive mode to transmitmode (STEP 814). The timing processor 308 waits for a determination thatthe transceiver 300 is to transition from receive mode to transmit mode.Upon making the determination that the transition is to occur, thetiming processor 308 causes V_(on) to transition from a relatively highvoltage to a relatively low voltage (STEP 816). V_(on) is applied to thetiming control circuit 310 (STEP 818). The timing control circuit 310inverts V_(on) to generate V_(on) (STEP 820). V_(on) is coupled to thecontrol port of the through switch 112 and turns the through switch 112on (STEP 822). V_(on) is coupled to the control port of the shunt switch118 and turns the shunt switch 118 off (STEP 824). In some embodiments,the timing control circuit 310 generates V_(on) with a delay relative toV_(on) that is equal to the propagation delay through the timing controlcircuit 310 with the FET 410 turned on. The process then returns to STEP802 and may toggle between transmit and receive mode as this processcontinues to cycle through the steps 802 through 824.

As should be readily apparent to one of ordinary skill in the art,various embodiments of the invention can be implemented to meet a widevariety of specifications. Thus, selection of suitable component valuesis a matter of design choice (so long as the frequencies of interestmentioned above can be handled). The switching and passive elements maybe implemented in any suitable integrated circuit (IC) technology,including but not limited to MOSFET and IGFET structures. Integratedcircuit embodiments may be fabricated using any suitable substrates andprocesses, including but not limited to standard bulk silicon,silicon-on-insulator (SOI), silicon-on-sapphire (SOS), GaAs pHEMT, andMESFET processes. Voltage levels may be adjusted or voltage polaritiesreversed depending on a particular specification and/or implementingtechnology (e.g., NMOS, PMOS, or CMOS). Component voltage, current, andpower handling capabilities may be adapted as needed, for example, byadjusting device sizes, “stacking” components to handle greatervoltages, and/or using multiple components in parallel to handle greatercurrents.

A number of embodiments have been described. It is to be understood thatvarious modifications may be made without departing from the spirit andscope of the claimed invention. For example, some of the steps describedabove may be order independent, and thus can be performed in an orderdifferent from that described. It is to be understood that the foregoingdescription is intended to illustrate and not to limit the scope of theinvention, which is defined by the scope of the following claims, andthat other embodiments are within the scope of the claims.

What is claimed is:
 1. An input control circuit for a low noiseamplifier, including: (a) a through switch configured to receive a radiofrequency (RF) signal and selectively settable to pass the received RFsignal to a terminal or block the received RF signal from the terminal;and (b) a shunt switch coupled between the terminal and circuit groundand configured to selectively suppress transient voltages at theterminal after the through switch is set to pass the received RF signalto the terminal.
 2. The input control circuit of claim 1, furtherincluding an LNA having an input coupled to the terminal.
 3. The inputcontrol circuit of claim 2, further including a bias control circuithaving a control input and a bias output, the bias output coupled to theLNA input and the bias output providing a bias signal in response toinputs applied to the control input of the bias control circuit.
 4. Theinput control circuit of claim 1, further including a three-portcirculator having a first circulator port configured to be coupled to anantenna, a second circulator port coupled to a transmit amplifier, and athird circulator port being coupled to the through switch.
 5. An inputcontrol circuit for a low noise amplifier, including: (a) a throughswitch configured to receive a radio frequency (RF) signal andselectively pass the received RF signal to a terminal in response to afirst control signal; and (b) a shunt switch coupled between theterminal and circuit ground and configured to selectively couple theterminal to circuit ground in response to a second control signal;wherein the second control signal causes the shunt switch to transitionfrom closed to open only after the first control signal causes thethrough switch to transition from open to closed.
 6. The input controlcircuit of claim 5, wherein the shunt switch remains closed after thefirst control signal causes the through switch to transition from opento closed for an amount of time sufficiently long to suppress transientvoltages at the terminal.
 7. The input control circuit of claim 5,wherein the through switch includes at least one field effect transistor(FET) having a capacitance when open and wherein the shunt switchremains closed after the first control signal causes the through switchto transition from open to closed for an amount of time sufficientlylong to permit a substantial amount of the charge accumulated in thethrough switch capacitance to discharge through the shunt switch.
 8. Theinput control circuit of claim 5, further including an LNA having aninput coupled to the terminal.
 9. The input control circuit of claim 8,further including a bias control circuit having a control input and abias output, the bias output coupled to the LNA input and the biasoutput providing a bias signal in response to inputs applied to thecontrol input of the bias control circuit.
 10. The input control circuitof claim 5, further including a three-port circulator having a firstcirculator port configured to be coupled to an antenna, a secondcirculator port coupled to a transmit amplifier, and a third circulatorport being coupled to the through switch.
 11. An input control circuitfor a low noise amplifier, including: (a) a through switch configured toreceive a radio frequency (RF) signal and selectively pass the receivedRF signal to a terminal; (b) a shunt switch coupled between the terminaland circuit ground and configured to selectively couple the terminal tocircuit ground; and (c) a timing control circuit coupled to the shuntswitch and configured to transition the shunt switch from a closed stateto an open state only after the through switch transitions from an openstate to a closed state.
 12. The input control circuit of claim 11,wherein the shunt switch remains closed after the through switchtransitions from an open state to a closed state for an amount of timesufficiently long to suppress transient voltages at the terminal. 13.The input control circuit of claim 11, wherein the through switchincludes at least one field effect transistor (FET) having a capacitancewhen open and wherein the shunt switch remains closed after the throughswitch transitions from an open state to a closed state for an amount oftime sufficiently long to permit a substantial amount of the chargeaccumulated in the through switch capacitance to discharge through theshunt switch.
 14. The input control circuit of claim 11, furtherincluding an LNA having an input coupled to the terminal.
 15. The inputcontrol circuit of claim 14, further including a bias control circuithaving a control input and a bias output, the bias output coupled to theLNA input and the bias output providing a bias signal in response toinputs applied to the control input of the bias control circuit.
 16. Theinput control circuit of claim 11, further including a three-portcirculator having a first circulator port configured to be coupled to anantenna, a second circulator port coupled to a transmit amplifier, and athird circulator port being coupled to the through switch.